1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the invention relates to a fuse box incorporated within a semiconductor device and a method of fabricating same.
2. Description of the Related Art
The development of contemporary semiconductor memory devices is characterized by ever increasing integration density. As the size of individual components and elements shrinks and as elements and components are placed closer and closer together the risk of fabrication defects increases. That is, as the separating margins between adjacent elements and components decreases in densely integrated semiconductor devices, the risk of fabrication errors causing critical operating defects increases. Such defects reduce manufacturing yields and negatively impact profitability of manufacturing operations.
One approach to mitigating the effect of increased fabrication defects is the provision of certain redundancy circuits. This is particularly true for semiconductor memory devices which include a large number of identical memory cells. If one memory cell within a memory cell array is non-operative due to a fabrication defect, a redundant memory cell selected from a group of redundant memory cells (i.e., a redundancy circuit) may be used in its place.
A common approach to replacing a defective cell with a redundant cell begins by running a test routine for all memory cells in an array. Once located, a defective memory cell is replaced by a redundant memory cell by cutting a corresponding fuse within a fuse box associated with the memory array. Fuse cutting may be accomplished using a laser. This approach has provided so successful that redundant memory cell arrays and associated fuse boxes are routinely incorporated into contemporary semiconductor memory devices.
Many contemporary semiconductor devices are also characterized by the incorporation of a final passivation layer (e.g., a silicon nitride layer having a hard layer quality) formed on an outermost side portion of the device. This final passivation layer protects the internal semiconductor elements and components from externally applied mechanical impacts and the intrusion of moisture and contaminates.
However, the final passivation layer and certain intervening insulating layers formed on the fuse box must be removed during fuse cutting operations. Removing the final passivation layer may expose, for example, interlayer insulating layers to the external environment. Some commonly used interlayer insulating layers such as silicon oxide are quite vulnerable to the effects of humidity. Thus, when the humidity permeates such interlayer insulating layers, internal interconnects may erode to the point where the reliability of the semiconductor device can not be assured. In order to block humidity permeation through interlayer insulating layers exposed during fuse cutting operations, a metal guard ring is formed around a fuse opening through which fuse cutting operations are performed.
Along with other elements and components of contemporary semiconductor devices, the pitch separating adjacent fuses has been decreased with increased integration. Thus, an adjacent fuse may be damaged during a fuse cutting operation if the intensity of the cutting laser is too great. Alternately, if the intensity of the cutting laser is too weak, the intended fuse will not be cut. As a remedy to the problems associated with accurate application of a cutting laser, the interlayer insulating layers overlaying the fuse box opening are over-etched with removal of the final passivation layer prior to fuse cutting operations, so that an upper portion of a metal layer forming the fuse pattern is also partially removed to decrease the height of the fuse pattern.
However, when the interlayer insulating layers are over-etched to decrease the height of the fuse pattern, the metal guard ring may become exposed. When the guard ring is exposed, melted metal portions of the cut fuse may contact and adhere to the guard ring. Such splatter protrusions may form a conductive bridge between a fuse in the fuse box and the guard ring. Figure (FIG.) 1 is a photograph showing a bridge (i.e., the same protrusion shown in the circle) produced between the fuse pattern and the guard ring by a fuse cutting operation. Because the guard ring is formed from a conductive metal, the cut fuse which is intended to form an open circuit may, in fact, be electrically connected through the bridge and the guard ring to an unintended circuit. This erroneous “connection” may cause a serious malfunction with the redundancy circuit.